The present invention relates to a multi-color display device and a process of fabricating the multi-color display device using color filters and, more particularly, to a process of fabricating the multi-color display device provided with color filters which are made of polymer layers formed by electro-deposition.
FIG. 1 shows one example of a conventional multi-color display device which makes use of color filters. In FIG. 1 numeral 1 indicates a transparent substrate; numeral 2 a display electrode made of a transparent conductive film; numeral 3 a color filter formed in close contact with the surface of the display electrode 2; numeral 4 a transparent counter electrode; and numeral 5 a transparent rear substrate. The space between the two substrates 1 and 5 is filled with a substance which functions as an optical shutter which can be opened or closed by the application of a voltage, such as a liquid crystal or an electrochromic material, and the color filters 3, 3' and 3" are formed to have different colors. Several colors can be displayed by selectively applying a voltage between the display electrodes 2, 2' and 2" and the transparent counter electrode 4.
This multiplication of the colors of a display using color filters is very effective in practice because it is considered that the method is convenient, any color can be easily obtained, and this color multiplication can be used in combination with various display materials and systems.
However, when fabricating this multi-color display device using color filters, no discrepancy can be allowed between the patterns on the display electrodes and the patterns on the color filters formed on the surfaces of the display electrodes. Especially when realizing a color graphic display using fine patterns in the three primary colors, duplicating the patterns of the display electrodes and the color filters presents a serious problem which makes the fabrication difficult. Another problem concerns color changes during the formation of the various colors, which complicates the process. In particular, if the coloration is effected by a dyeing method, resist-printing steps are needed, which make the fabrication process more complex. Namely parts which have already been dyed should not be dyed again in subsequent dyeing steps. Moreover, the resist printing technique itself presents difficult problems which must be solved for each dye.
Methods of forming the color filters that have been considered, generally speaking, use means such as screen printing or photolithography. Screen printing does not require any resist printing, but has limitations concerning size reduction so that positional accuracy becomes worse as the number of colors increases, with resultant discrepancies in the display pattern. Photolithography can produce fine patterns but a photolithographic step is necessary for each change of color, and resist printing is also needed to prevent re-dyeing so that the process becomes very complicated and the advantage of a convenient color-increasing means is lost.
The color filters obtained by the above mentioned methods are made of insulator layers, and the display device is formed in such a way that an insulator is sandwiched between a display electrode and display material. Losses in the drive voltage are caused by the drops in voltage across the color filters, thus obstructing the drive at low voltages.